“Nightcaps” come in all shapes and sizes. Some people like to have a drink before bed, and others prefer taking a nice long toke. But while these nightcaps may help you fall asleep faster, they may not be giving you the rest your mind and body actually needs.

Generally speaking, having a little alcohol or marijuana here and there probably isn’t going to cause you any major health problems. But both substances affect your sleep, and sleep is a major component of your physical and mental health. To get to the bottom of what these substances do, we spoke with Dr. Nitun Verma, a specialist in sleep medicine and Chief Medical Officer of Peerwell, a company treating chronic disease.

What Good Sleep Looks Like (and Why It’s Important)

Before we can talk about how alcohol and marijuana affect your sleep, let’s talk about what “good sleep” really is. Most adults need somewhere around seven or eight hours of sleep every night. But there’s a big difference between being unconscious for eight hours and actually getting restful sleep. When you slumber, you ideally go through four main stages of sleep without interruption:

NREM 1 (N1): Also known as “non-rapid eye movement 1,” or “light sleep.” Your body temperature, heart rate, breathing rate, and energy use all decrease across the board. Your muscles are still active and you can still produce reactions to environmental stimuli. Essentially, you are falling asleep.

NREM 3 (N3): Deep sleep or “slow-wave” sleep. Environmental stimuli are no longer likely to produce any reactions. Thought to be the most restful stage of sleep, and accounts for about a quarter of your sleep time. This stage leads into the fourth stage and is sometimes considered to be a part of the fourth stage as well.

REM (rapid eye movement): Also known as the “dream state.” Your muscles become paralyzed and your breathing and heart rate become unregulated. The true function of REM sleep is unknown, but missing it can impair your ability to learn complex tasks. This stage accounts for about a quarter of your sleep time as well.

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On a good night of sleep, you’ll go through each stage multiple times within several cycles that last about 90 minutes each. Ideally, the process goes in this order: N1, N2, N3, N2, REM. Then it repeats. In an eight hour sleep session, you’ll go through the whole process about four or five times, with each stage lasting a different length of time within each cycle. Dr. Michael Twery, a sleep expert at the National Institutes of Health, explains that when the cycle is disturbed or altered in some way, you miss out on sleep’s restorative benefits, even if you are putting in the time. You could literally be wasting your time unconscious, and making your day tomorrow more difficult. Talk about a crappy deal.

According to Dr. Merrill Mitler, a sleep expert at the National Institutes of Health, aiming for your seven to eight hours every night is essential if you want to have a better mood and maintain higher levels of reasoning, problem-solving, and attention to detail. Mitler also suggests that getting good sleep means having quicker reflexes and reduces your chance of being involved in a traffic accident. Good sleep affects every tissue in your body, including your immune system, growth and stress hormones, appetite, breathing, blood pressure, and cardiovascular health.

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The bottom line: your body needs sleep, and it needs that “good sleep” where it can go through all the normal stages and cycles. Both alcohol and marijuana can alter those sleep stages.

How Alcohol Affects Your Sleep

Alcohol shortens the time to fall asleep and arousal threshold changes (while under the influence little noises don’t wake you up). It wears off in the middle of the night so your arousal threshold changes. This is bad because little noises and things wake you up more and the second half of sleep is pretty low quality.

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Essentially, alcohol is helping you get to NREM (N1) faster and it makes you more capable of ignoring environmental stimuli so you can doze off. As Verma explains, however, the effects don’t last forever. Your body is still attempting to process the alcohol and remove it from your system.

Francis Crick (of DNA fame) and Grahame Mitchison suggested that dreams act as an “unlearning” mechanism, whereby certain modes of neural activity are erased by random activation of cortical connections... By analogy, these “parasitic” modes of activity might be unwanted thoughts or erroneous information, which, if not expunged, could become the basis for obsession, paranoia, or other pathologies of thought that prevent the “system” from working as efficiently as it should. In a different vein, Michel Jouvet proposed that dreaming reinforces behaviors not commonly encountered during the awake state (aggression, fearful situations) by rehearsing them while dreaming. Yet another hypothesis is that REM sleep and dreams are involved in the transfer of memories between the hippocampus and neocortex.

Despite the mystery, researchers know that REM sleep is important, and any inconsistency in any sleep stage can throw all the other stages out of whack. According to Verma, this can be especially troublesome for someone who is trying to quit smoking and likes to have a drink every night. As Verma has told us in the past, consistency is the key to getting good sleep. Anything that alters that, despite the amount of time you sleep, can be harmful to your beauty rest.

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How Marijuana Affects Your Sleep

Marijuana is known for it’s calming effects that can often lead to drowsiness, but despite its popularity, there’s not as much research on its relationship with sleep. Still, there’s enough to draw a few conclusions.

For starters, Verma explains that marijuana also messes with your REM sleep. Unlike alcohol, however, marijuana doesn’t cause REM fragmentation; it just reduces the amount of REM sleep you get. According to a study published in Sleep Medicine Reviews, smoked marijuana and orally ingested tetrahydrocannabinol (or THC, the active ingredient in marijuana) reduced REM sleep across the board. That means the more you consume, the less likely you are to dream. The first couple times you partake you might still be able to dream, but over time researchers believe that habitual ingestion will suppress your REM sleep significantly. And, according to the study, once you stop your sleep is likely to suffer:

Difficulty sleeping and strange dreams are among the most consistently reported symptoms of acute and subacute cannabis withdrawal. Longer sleep onset latency, reduced slow wave sleep and a REM rebound can be observed.

Essentially, as Verma clarifies, marijuana can shorten the time it takes to fall asleep, but if you don’t do ingest or smoke it consistently, you’ll take longer to fall asleep. You’ll also likely experience an REM rebound, which means you’ll dream more the first few nights after you stop using. Like letting go of a pinched garden hose, your nights will be filled with vivid dreams; and depending on your state of mind, that could mean a blissful night of adventure or a troublesome night of intense nightmares. Furthermore, it can increase slow-wave (NREM 3) deep sleep, which is good because that’s where experts believe most of your actual recuperation takes place. However, as you continue to consume, your slow-wave sleep will get severely reduced, reducing the restfulness your sleep is supposed to provide.

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According to a study published in Biological Psychiatry, the first four days of regular marijuana consumption can see an upward spike in slow-wave sleep. Then by the eighth day, slow-wave sleep can dip significantly, continuing to dip even if you stop using. Essentially, your body begins to go through mild symptoms of withdrawal. The symptoms are pretty tame compared to other drugs, but how long they last depends on how long you’ve used and how often. The withdrawal period could last anywhere from a couple days for occasional users to several weeks for daily users. This all leads to a gnarly catch-22:

If you start, you’ll get great rest—at first.

If you don’t stop, you’ll eventually get less restful sleep, missing out on most of your deep sleep, despite how long you’re down for the count.

If you do stop, falling asleep will be much harder at first, and your dreams will be far more intense for a few days to a few weeks after you stop regular use.

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None of this is to say that marijuana is bad. It’s a huge help for a lot of people who suffer from anxiety, chronic pain, and even severe insomnia. Many doctors even prescribe it for insomnia and anxiety-related insomnia, where it’s legal for consumption. And when you can’t sleep at all, some sleep is still better than none.

If you’re a recreational user, however, it’s all about moderation. Habitual use can mess with your sleep cycle, so it can be advantageous to take breaks throughout the week or poke your head out of the clouds every couple of weeks. Not because pot fries your brain like an egg in a bad 80s commercial, but because getting good sleep is important to your health.